1. Field of the Invention
The invention in general relates to flowmeters, and particularly to an acoustic flowmeter for obtaining volumetric flow rates to a high degree of accuracy in the presence of varying Reynolds number.
2. Description of the Prior Art
A variety of systems exist for measuring velocity or volumetric flow rate of a fluid in a pipe. Many of these systems utilize the propagation of acoustic energy through the fluid in the pipe to obtain the desired readings. In some systems, acoustic energy is propagated from an upstream transducer to a downstream transducer, and vice versa, and the difference in transit times of the oppositely directed acoustic energy is utilized in the computation of fluid flow. Other systems for example use the difference in phase of oppositely directed acoustic signals while still other systems utilize a sing-around technique either along a single path or along two closely-spaced parallel paths, to obtain a frequency difference indicative of fluid flow.
For highly distorted fluid flow and situations where the fluid is subject to variations in the velocity profile, use is made of an acoustic system having a plurality of acoustic paths provided at specific locations, with the individual flow readings from each path being combined according to a numerical integration technique such as the Gaussian technique to compute volumetric flow rate.
It is often desirable, however, from an economic standpoint to utilize a less expensive, single path system (or a two path sing-around system) rather than a multipath system as in the Gaussian technique. In single path systems generally, a peak velocity indication is obtained and this value must be modified by some meter factor in order to obtain mean velocity. The meter factor, however, is calibrated for a particular velocity profile which in actuality changes with Reynolds number, which for a given pipe diameter and fluid varies with velocity.
Generally, in a system in which velocity is obtained along a diametrical path, operation is predicated upon a particular fixed Reynolds number. However, a Reynolds number variation of from 1.times.10.sup.4 to 1.times.10.sup.7 would cause a change of 4% in the meter factor. To compensate, some systems take measurements along a chordal path located at a certain distance from the center of the pipe, where readings are relatively insensitive to profile changes.
There are advantages to be able to mount the transducers relative to the pipe so as to obtain a reading along a diametrical path and the present invention provides for a highly accurate flowmeter system including such placement, even in the presence of varying Reynolds number.